Objectives To determine the role of prolactin in male parental care for the cot Prolactin (PRL) levels have been elevated during male parental care in some monogamous birds, rodents and one primate, the common marmoset, Callithrix jacchus. We examined PRL levels in six male cotton-top tamarins (Saguinus oedipus) which are socially monogamous and begin caring for infants shortly after birth. Urine samples were collected, concentrated and analyzed two weeks before and following birth of infants to their mate and in nonparental males paired with females, nonparental males living adjacent to a female and in eldest sons in large family groups. PRL levels were significantly higher in fathers during the postpartum period than in the other males. PRL levels in fathers were elevated before birth, following birth and after infants were weaned. The elevated PRL levels in parental males appeared to be related to the experience of the fathers since correlations between PRL levels and the number of successful births a father had experienced, the number of previous births or the age of the father were high. However, correlations between PRL levels for individual fathers and the percent of time fathers carried infants or the number of helpers in the group were low. Elevated PRL in fathers was not associated with elevated cortisol levels. However, both cortisol and PRL were elevated following capture plus saline injection or metoclopramide injection indicating that PRL does respond to acute stress. Theses results suggest that different neural pathways are probably involved in PRL release during parental care versus response to acute stress. Keywords urinary prolactin, urinary cortisol, parental care, stress